Equity (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	$ (314,948)
Income tax benefit (expense)	(1,201,099)	$ 680,493	$ 8,285
Ending Balance	(90,124)	(314,948)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	(78)	(65)	(30)
Change in OCI before reclassifications	109	(20)	(54)
Amounts reclassified from AOCI	0	0	0
Income tax benefit (expense)	(38)	7	19
Ending Balance	(7)	(78)	(65)
Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	(314,870)	46,231	84,652
Change in OCI before reclassifications	320,182	(469,356)	(54,279)
Amounts reclassified from AOCI	3,177	(86,184)	(4,831)
Income tax benefit (expense)	(98,606)	194,439	20,689
Ending Balance	(90,117)	(314,870)	46,231
Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	(314,948)	46,166	84,622
Change in OCI before reclassifications	320,291	(469,376)	(54,333)
Amounts reclassified from AOCI	3,177	(86,184)	(4,831)
Income tax benefit (expense)	(98,644)	194,446	20,708
Ending Balance	(90,124)	(314,948)	46,166
Cash flow hedges \| Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	12,000	15,000
Ending Balance	$ (26,000)	$ 12,000	$ 15,000

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

Amount before tax and reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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Amount before tax of reclassification adjustments of other comprehensive income (loss).

+ References

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